The Presence of HCO3- Does Not Inhibit Alpha-Adrenergic Increases in Proximal Tubular Intracellular pH

Publisher Website
Google Scholar
Abstract
Hormonal stimulation of Na+/H+ exchange increased intracellular pH (pHi) in a dose-dependent manner in proximal tubules suspended in Krebs-Henseleit buffer (KHB) supplemented with 25 mM HCO3- and CO2 (KHB+HCO3). The maximum increase in pHi was approximately 45% of the response observed with segments suspended in bicarbonate-free buffer (KHB-HCO3) and the time required to achieve maximum pHi alterations was significantly increased (p < 0.05) in the presence of KHB + HCO3 when compared to responses obtained in KHB-HCO3. Dose-response curves for agonist-induced pH increases were shifted to the right by a factor of 10 for segments suspended in KHB + HCO3. Increases in pH, induced by agonists in KHB + HCO3 were effectively blocked by pretreatment with 10 µM ethylisopropyl amiloride but not with the Cl-/HCO3- inhibitor, DIDS (0.1 mM, 30 min). We conclude that stimulation of α-adrenergic receptors on proximal nephrons increased pH, due to activation of Na+/H+ exchange and can be detected in the presence of HCO3- although the time course and maximum level of change differ significantly from those observed in a HCO3--free buffer.